The gray-short-tailed opossum, M. domestica, has been established as a model organism for comparative biomedical research on a broad range of topics that are relevant to human development, physiology, and disease susceptibility. However, a lack of basic information on fundamental genetic characteristics limits its potential for inquiries involving the genetic regulation of normal developmental and physiologic processes, and the influences of genetic variation on health-related physiologic characteristics. To mitigate this situation, a map of the M. domestica genome will be constructed that can be used to detect, map, and ultimately isolate and clone genes that influence normal and abnormal phenotypic variation. The overall objectives are to construct a linkage map of 200 or more polymorphic marker loci, to use physical mapping studies to anchor the linkage map on the physical genome, and to use the map to determine the locations of one or more genes that influence variable responsiveness of dietary cholesterol and fat. The Specific Aims are to: 1) expand the number of anonymous and functional gene markers on the existing, sparsely-filled linkage map through continuing linkage studies utilizing an existing backcross mapping panel; 2) complete a 5 cM linkage map by creating, and utilizing for mapping, a new backcross mapping panel designed to maximize opportunities for the detection and mapping of polymorphisms at functional gene loci; 3) develop a physical map showing the locations and orientations of known linkage groups on M. domestica chromosomes; and 4) detect and map one or more of the genes responsible for highly heritable variation in diet-induced hypercholesterolemic responsiveness that occurs in this species. The linkage map, comprised of polymorphic genetic marker loci including anonymous micosatellite loci and functional genes, will be developed by analysis of intergenic recombination rates determined from genotype analyses of offspring from two large backcross family panels. Fluorescence in situ hybridization (FISH) will be used to locate the physical positions of the known linkage groups on individual chromosomes. Parametric LOD-score linkage analyses and pedigree based variance components methods will be used to seek linkage between marker genes on the linkage map and genes that influence plasma lipoprotein phenotypes in a family panel that has been subjected to a dietary challenge regimen.